1. Field
This disclosure relates to a method for preparing nanocrystal-metal oxide composites, methods of manufacture thereof, and to articles comprising the same. In one embodiment, the article is a light-emitting device (LED). More specifically, the method comprises mixing nanocrystals, a first metal oxide precursor, a solvent and water to form a sol-gel composite, and reacting the sol-gel composite with a second metal oxide precursor.
2. Description of the Related Art
In general, the luminescence and electrical properties of nanocrystals can be controlled by varying various parameters, such as, for example, the size and composition of the nanocrystals. As a result of the ability to vary these properties, nanocrystals have found application in various industrial fields, including light-emitting devices, solar cells, sensors, memory devices and other devices.
A semiconductor nanocrystal, also called a “quantum dot”, is a crystalline material having dimensions that are of the order of a few nanometers. Since such nanometer-sized materials have large surface areas per unit volume, most of the constituent atoms of the material are present at the surface of the material and as a result, quantum confinement effects are observed in the material. Semiconductor nanocrystals generally absorb light from an excitation source to reach an excited state of energy and radiate energy corresponding to the energy band gap of the semiconductor nanocrystals. Thus, the structural and optical properties account for unique electrical, magnetic, optical, chemical and mechanical properties of semiconductor nanocrystals and these properties are different from those inherently displayed by bulk semiconductor materials having similar compositions.
In summary, the physical size or chemical composition of semiconductor nanocrystals are factors that determine the energy band gap of the semiconductor nanocrystals. Devices (e.g., displays and biological probes) are currently being developed that take advantage of the various energy levels of semiconductor nanocrystals.
Vapor deposition processes such as metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) have been used to synthesize nanocrystals. Wet chemical methods are also used for growing nanocrystals from precursor materials that are dispersed in an organic solvent.
One of the disadvantages of nanocrystalline materials are that the nanocrystals are susceptible to oxidation and also tend to undergo agglomeration upon the application of certain external stimuli. These tendencies to undergo oxidation and to agglomerate make the nanocrystals unsuitable for use in practical applications.